1. Field of the Invention
The present invention relates to a multi-component force measurement spindle unit capable of measuring the various characteristics of tires.
2. Description of the Related Art
Generally, a known tire testing machine produces the contact state between a tire and a road surface in a simulated manner and measures forces and moments exerted on the tire by the road surface. The tire testing machine brings the tire supported by the spindle shaft of a spindle unit into contact with a rotation drum, etc., serving as the road surface in a state where predetermined loads are applied to the tire. Then, the tire testing machine measures a force (load) and a moment in each direction, which act on the rotating tire via the rotation drum, etc., with a multi-component force measurement sensor incorporated in the spindle unit.
For example, it is assumed that the pressing direction of the tire onto the rotation drum is a z-direction, the traveling direction (tangent line direction) of the tire is an x-direction, and a direction along the rotation shaft of the tire is a y-direction. In this case, the general tire testing machine can measure a force Fz (grounding load) directed to the z-direction, a force Fx (front-and-rear direction force or rolling resistance force) directed to the x-direction, a force Fy (cornering force) directed to the y-direction, a moment Mz (self-aligning torque) around the axis directed to the z-direction, a moment Mx (overturning moment) around the axis directed to the x-direction, a moment My (rolling resistance moment) around the axis directed to the y-direction, etc.
A strain gauge type has been often used as the above multi-component force measurement sensor. As described in, for example, Japanese Patent Application Publication No. S57-169643, the multi-component force measurement sensor of strain gauge type is structured such that a force applied body provided on the inner periphery side and a fixed body provided on the outer periphery side are connected to each other via a plurality of bar-like strain elements extending in the radial direction. The multi-component force measurement sensor detects the deformation of the strain elements with strain gauges to measure forces and moments acting on a tire.
As a tire testing machine using such a multi-component force measurement sensor, there has been known one described in, for example, Japanese Patent Publication No. 4310365. In the tire testing machine, the multi-component force measurement sensor is provided at either end of a housing (hereinafter referred to as inner sleeve) in the axial center direction, and the housing is supported by the multi-component force measurement sensors provided at two places with a space therebetween in the axial center direction. A force applied body on the inner periphery side of each of the multi-component force measurement sensors is fixed to the inner sleeve. In addition, a fixed body on the outer periphery side of the multi-component force measurement sensor is fixed to a support frame (base substance) or the like supporting a spindle unit, via a housing holding member (hereinafter referred to as outer sleeve). Thus, forces and moments acting on a tire are transmitted to strain elements via the inner sleeve to cause the deformation of the strain elements, and strain gauges detect the deformation of the strain elements to measure the forces and the moments acting on the tire.
Further, as a tire testing machine having only a single multi-component force measurement sensor, there has been known one described in, for example, Japanese Patent Application Publication No. 2003-4598. The tire testing machine has a spindle that brings a testing tire into pressure-contact with the outer periphery of a running drum. The spindle is attached at the center of the rotation shaft of the tire and supports the tire via bearings. In the tire testing machine, the multi-component force measurement sensor provided at a position apart from the tire of the spindle by a predetermined distance in the axial center direction of the spindle measures the relationship between the axle load Fz and the rolling resistance Fx of the tire to carry out a rolling resistance measurement method for the tire. In the tire testing machine, a spindle shaft is fixed to a support frame via the multi-component force measurement sensor so as not to rotate. Further, the tire is rotatably attached to one end of the spindle shaft via the bearings.
The spindle unit described in Japanese Patent Publication No. 4310365 is in a state where the translating and rotating motions of the spindle unit are constrained between the two multi-component force measurement sensors, i.e., the spindle unit is in a statistically intermediate state or in an overconstrained state.
In addition, bearing parts rotatably supporting a spindle shaft are provided between the inner sleeve and the spindle shaft. In the bearing parts, heat is generated with the rotation of the spindle shaft, and the generated heat is transmitted to both the inner sleeve and an outer sleeve. The inner sleeve and the outer sleeve are expanded by the heat thus transmitted, but the expanded states of the inner sleeve and the outer sleeve are different. The difference between the expanded states causes strains, and the strains act on both the multi-component force measurement sensors connected to the inner sleeve and the outer sleeve. That is, in the spindle unit in the overconstrained state between both the multi-component force measurement sensors, the strains resulting from the difference between the expanded state of the inner sleeve and that of the outer sleeve are caused in the multi-component force measurement sensors, and measurement errors corresponding to the strains are added to the measured values of loads and moments. Because of this, it becomes difficult to accurately measure the loads and the moments produced in the tire.
In order to avoid such a problem, the present inventors have attempted to provide a cooling mechanism that circulates the lubricating oil of bearing parts to positively cool the bearing parts. However, since heat is generated in the bearing parts in extremely large amounts, there was a case in which the heat generated in the bearing parts was not sufficiently removed with the cooling mechanism. In addition, it turns out that when the lubricating oil is supplied in large amounts to remove the heat, there may be a case that the lubricating oil is heated by stirring heat and heat is generated in the bearing parts.
Further, in the tire testing machine described in Japanese Patent Application Publication No. 2003-4598, the spindle shaft has a certain degree of length from one end to which the tire is attached in the axial center direction to the other end fixed to the support frame via the multi-component force measurement sensor. When loads act on the one end of the spindle shaft in a direction for pressing the tire onto the outer peripheral surface of the traveling drum, large moments are, of course, produced in the multi-component force measurement sensor provided at the other end of the spindle shaft. Therefore, the tire testing machine employs the multi-component force measurement sensor that can be resistant to large moments. Since such a multi-component force measurement sensor employs thick strain elements, etc., to resist acting large moments, the multi-component force measurement sensor cannot detect changes in minute force. As a result, the multi-component force measurement sensor is not allowed to perform detection with high accuracy.
A rolling resistance testing machine is required to detect changes in minute force acting on a spindle shaft with high accuracy. Therefore, it is desirable that a multi-component force measurement sensor used in the rolling resistance testing machine employ thin strain elements to a greater extent.
In view of this, the present inventors have attempted to hold a multi-component force measurement sensor close to a tire to reduce moments produced in the multi-component force measurement sensor. However, it turns out that when the multi-component force measurement sensor is held close to the tire, the influence of the heat generated in bearing parts becomes extremely large and thus the accuracy of the multi-component force measurement sensor is reduced. Therefore, the present inventors have attempted to provide bearing parts inside a housing on the side opposite to the tire with the multi-component force measurement sensor interposed therebetween, to cause a spindle shaft to be rotatably supported by the bearing parts, and to provide a cooling mechanism that circulates the lubricating oil of the bearing parts to positively cool the bearing parts. However, since heat is generated in the bearing parts in extremely large amounts, it may not be possible to sufficiently remove the influence of the heat generated in the bearing parts with the cooling mechanism. Moreover, it turns out that when the lubricating oil is supplied in large amounts to remove the heat, the lubricating oil is heated by stirring heat and thus the generation of the heat is spurred in the bearing parts on the contrary.
The present inventors have further studied over and over again and come to the following findings. When pressing forces act on a spindle shaft in a direction perpendicular to the spindle shaft, heat is likely to be generated only in part in the periphery direction of bearing parts supporting the spindle shaft. Therefore, compared with other parts in the periphery direction, the part in the periphery direction of the housing where the bearing parts are provided is thermally deformed on a large scale in the radial direction of the spindle shaft. Thus, the accuracy of a multi-component force measurement sensor is reduced.